1. Field of the Invention
This invention relates to apparatus for extracting tubes from the tube sheets of heat exchangers.
2. Description of the Prior Art
It is heretofore been proposed to provide a tube pulling spear externally threaded at one end for tube engagement with an internally threaded portion at the outer end for the reception of an extension rod to which a pulling mechanism can be connected.
Miller, in U.S. Pat. No. 3,613,212 shows a straight sided tap with a threaded end portion 12 and an elongated shank portion 13, the threads on the end portion being outwardly inclined as at 27 and 31 as shown in the drawings for contraction of the side wall of the tube. The other and outermost end of the shank portion 12 is threaded and has a head 20 for the reception of a tool for threading the tap into the tube to be withdrawn.
A nut 17 is provided for threaded engagement with the threaded outer end of the shank 13 with the spacer sleeve 15 interposed between the nut 17 and the tube sheet. The nut 17 has a socket extension 25 for connection to an impact wrench for rotation of the nut 17 for tube withdrawal.
Chuplis, in U.S. Pat. No. 3,120,700, shows a tube puller which includes a jack nut 2 with one end for engagement with the tube sheet and having an elongated internally threaded axial bore 4 therethrough with a hexagonal head 6 at the other end for engagement and turning by an impact wrench. A tap 8 is provided in the shape of an elongated stud with an externally threaded portion 10 for engagement in the bore 4, and an integral hexagonal head 16. A threaded tap 12 of reduced diameter is shown as of uniform diameter with a tapered entrance and an integral tap pilot 14. A tap driver 18 is employed having a shank 20 and a socket 22 for engagement with the head 16 for insertion of the tap portion 12 into the tube as shown in FIG. 3. The tap driver 18 is withdrawn and further turning of the head 6 of the jack nut 2 effects retraction of the tube as shown in FIGS. 4 and 5. FIG. 6 shows a modified form of jack nut 2' which includes a bearing 26.
Lassarat, in U.S. Pat. No. 4,095,335, shows an automatic tube puller which includes a threaded mandrel 48 which is screwed into a heat exchanger tube 50 by an impact tool or ratchet wrench after which the pulling device is applied to the mandrel for retraction of the mandrel 48 and the tube 50 with which the mandrel is engaged. The pulling device has an adapter tube 46 to engage the tube sheet. The threaded portion of the mandrel engageable with the tube is shown as of uniform diameter.
The devices heretofore available have various shortcomings. The Chuplis and Miller devices have straight sided taps which are threaded into the tube to be withdrawn by torque applied to exterior surfaces of a bolt head, the tap and tube being withdrawn by a jack screw utilizing a second set of screws on the back of the tap. While these devices are effective they are slow and awkward to use, require several manual operations and are not suited for use with hydraulic power pulling mechanisms. The length of the taps and their cylindrical cutting threads make it difficult to drive them in straight. This is critical since, because of the high force required for tube withdrawal, the extraction forces applied, particularly on elongated shanks and the like, and angular misalignment even slightly off center causes tap breakage. The greater the length the greater the offset for a given angular misalignment. In practice, also, many operators tend to drive the tap in too far with resultant tightening of the tube into the tube sheet.
The Lassarat device is alo subject to problems of misalignment and over driving as well as the difficulty of manually fitting the pulling device over the mandrel.
The structures heretofore available, also, because of their length are relatively complex and expensive and subject to tap breakage.